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Hydrogen Peroxide Activation over TiIV: What Have We Learned from Studies on Ti-Containing Polyoxometalates?

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  • Dedicated to Professor M. Pope on the occasion of his 80th birthday

Abstract

This short review paper summarizes recent findings in the field of H2O2 activation over TiIV centers on the basis of model studies of Ti-containing polyoxometalates (Ti-POM) that used both experimental and computational techniques. Alkene epoxidation with H2O2 mediated by two different POMs, the Ti-monosubstituted Keggin-type POM, [PTi(OH)W11O39]4– (1), and the Ti-disubstituted sandwich-type POM, [Ti2(OH)2As2W19O67(H2O)]8– (2), which contain well-defined six- and five-coordinate titanium atoms, respectively, as well as some other Ti-POMs, has been explored to elucidate the role of the TiIV coordination environment in this reaction. The effect of the Ti-POM protonation state on the mechanism of H2O2 activation has been analyzed in the context of its relevance to alkene epoxidation. The crucial factors that favor the heterolytic oxidation mechanism that leads to the selective formation of epoxides have been disclosed.

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